The present invention relates generally to magnetoresistive read, inductive write magnetic transducers and, more particularly, laminated sendust films and a process for fabricating such films suitable for use as shields and pole pieces in magnetic transducers.
In the magnetic recording industry, the drive towards increased recording density has led to the requirement for magnetic storage media having narrower data recording tracks, lower track pitch, i.e., more tracks per inch, and greater linear recording density along the data tracks. In turn, increased recording density places an ever increasing demand on the devices employed to record (write) and read the recorded information. With the increased recording density capability, the trend is towards magnetic media requiring greater magnetic field strength to accomplish the recording of data. Similarly, read transducers having greater sensitivity and reduced vulnerability to noise and cross-talk are desirable. At the present time, the most likely candidate to meet these requirement appears to be a magnetic transducer including an inductive write head and a magnetoresistive (MR) read sensor or head,
In order for an MR read head to be capable of reading recorded data from a magnetic medium at these high recording densities, the MR sensing element must be incorporated in the gap between two magnetic shielding elements. For example, U.S. Pat. No. 4,639,806 to Kira et al discloses an MR read head including a shielded MR sensing element, and further discloses that the shields elements may be fabricated of high permeability magnetic material such as nickel-zinc ferrite (NiZnFe), manganese-zinc ferrite (MnZnFe), an iron-silicon-aluminum alloy generally referred to as sendust or a nickel-iron alloy generally referred to as permalloy.
Typically in a rotating rigid magnetic disk storage system, the read/write transducer is mounted on the trailing edge of a flying slider which supports the transducer above the surface of the rotating disk in close proximity to the magnetic media. Various elements of the transducer, such as the MR sensing element and its associated magnetic shields for the MR head and the magnetic pole tips and the nonmagnetic material disposed therebetween forming the magnetic gap for the inductive head, are exposed at the slider air bearing surface (ABS) imposing strict design and materials requirements. The read and write head elements which are exposed at the ABS are susceptible to physical damage when the slider encounters asperities or contaminants which may exist on the surface of the magnetic recording disks.
Among the different conductive materials exposed at the MR head ABS, the leading magnetic shield element presents the most serious problem since the shield provides a large volume of conductive material which can be easily scratched or smeared to form a short circuit path between the leading shield and MR sensing elements, thereby resulting in sensor shorting.
In the inductive write head, as well as in inductive heads designed to provide both the read and write functions, the magnetic yoke which forms the magnetic circuit for the inductive coil terminates at the slide ABS in a pair of opposed pole tips separated by a transducing gap. While the majority of the yoke structure is of relatively large dimensions, the pole tips are relatively narrow and thin thus requiring that they be fabricated of a material having a high saturation magnetization and high permeability. As noted above, since the pole tips and the gap are present at the inductive head ABS, it is also a requirement that the pole tip material be of sufficient hardness to minimize smearing and scratching caused by asperities or contaminants at the magnetic media surface. Also, since the geometry of the yoke and head structure allows the major portion of the yoke to be away from the ABS and thus not exposed to the harsh conditions present at the ABS, it is common practice to fabricate only the pole tips of materials having the properties required to survive at the ABS.
It is well-known in the prior art to utilize sendust as the material for both the leading shield in MR heads and for the pole tip structures in inductive heads. For example, U.S. Pat. No. 4,918,554 granted to Bajorek et al discloses a process for manufacturing a shielded MR sensor having the leading shield composed of sendust. Similarly, U.S. Pat. No. 4,780,779 granted to Pisharody et al discloses laminated sendust pole tip structures in an inductive magnetic head for video recording. Because of its excellent soft magnetic properties, thermal stability and mechanical integrity, hardness in particular, sendust alloys (Si: approximately 9.6%, Al: approximately 5.4%, Fe: approximately 85%) in bulk form is a preferred choice for shield elements and pole tip structures in MR/inductive thin film heads and for core material in metal-in-gap (MIG) ferrite heads. On the other hand, sendust films having good anisotropic properties and desirable mechanical properties such as magnetostriction tend to be very difficult to fabricate. Various aspects of this problem have been explored and and solved. For example, U.S. Pat. No. 4,897,318 granted to Sakakima et al discloses laminated structures of FeSi alloy films and sendust films wherein the magnetostriction coefficient is controlled to provide a high wear resistance and a high saturation magnetization. Japanese Application No. 1-342595, Publication No. 3-203008 published Sep. 4, 1991, discloses a laminated sendust structure in which a chromium (Cr) seed layer is utilized to orient the structure of subsequent sendust layers to provide improved soft magnetic characteristics. European Patent No. 0 159 028 B1, European Application No. 85104637.5 published Oct. 23, 1985, discloses thin films of a sendust-based alloy uniformly doped with a specified amount of oxygen (O) and having improved magnetic permeability and hardness.
The magnetic properties of sendust thin films of particular importance to MR and inductive head structures, such as magnetostriction, anisotropy field and coercivity, for example, strongly depend on the composition of the sendust material. Utilizing present deposition processes, films having good anisotropy field and magnetically soft characteristics can be obtained over only a relatively narrow composition range for sendust alloys.